The present invention relates to a volume reduction filling member for a microphone for preventing a generation of a cavity resonance of a unidirectional condenser microphone, and a unidirectional condenser microphone incorporating the same.
Generally, a condenser microphone unit is formed by a unit case whose one face includes a front acoustic terminal as a sound introduction hole and is closed, whereas a female screw is incised on an inner periphery face of an open end portion dividing the other open face. In an order starting from a front acoustic terminal side inside the unit case toward the open end portion, a diaphragm ring including a diaphragm; a spacer ring; and a fixed electrode and an insulating seat relative to the diaphragm are housed. A lock ring is screwed through a male screw screwed into the female screw on a back face of the insulating seat, so that the fixed electrode can be pressed and fixed to a diaphragm ring side through the insulating seat with a predetermined pressure.
FIG. 3(a) and FIG. 3(b) are explanatory drawings showing one example of a unidirectional cylindrical condenser microphone formed by housing the conventional condenser microphone unit as mentioned above inside a cylindrical body, wherein FIG. 3(a) shows a right side view, and FIG. 3(b) shows a front view, respectively.
According to the aforementioned figures, a unidirectional condenser microphone 51 is formed by a microphone cylindrical body 52 including rear acoustic terminals 54 on a peripheral face of a front end portion 53 thereof; and a condenser microphone unit 57 including front acoustic terminals 58 on a tip face 57a and screwed and disposed on a front end side of the microphone cylindrical body 52.
Also, inside the microphone cylindrical body 52, there is disposed a circuit substrate (not shown in the figures) electrically connected to an output connector portion housed and disposed on a back end portion 56 side thereof in a state wherein a tip portion side thereof is held by a holding member.
Namely, inside the cylindrical body 52, a space for housing and disposing an electronic circuit member including the circuit substrate is required. As a result, after the electronic circuit member and the circuit substrate are disposed at predetermined positions, at portions where the rear acoustic terminals 54 are positioned, there remain a cavity communicating with outside air through the rear acoustic terminals 54.
Then, the cavity operates as an acoustic capacity, so that in the rear acoustic terminal 54, there is an acoustic mass. Therefore, a resonance is generated so as to have a problem of deteriorating a directional frequency response.
FIG. 4 depicts FIG. 1(a) in Japanese Patent Application Publication No. 2011-9807 proposed in order to solve the problem mentioned above. Inside a cavity 55 of the microphone cylindrical body 52 in the unidirectional condenser microphone 51, there is disposed a volume reduction filling member 60 for a microphone. Also, the volume reduction filling member 60 for a microphone is supported in a holding member 63. In a center axis direction of the volume reduction filling member 60 for a microphone, there is fixed and disposed an electrode extraction member 61. The electrode extraction member 61 presses a fixed electrode 59 side forming the condenser microphone unit 57. The volume reduction filling member 60 for a microphone is housed and disposed inside the cavity 55 in order to reduce a volume of the microphone cylindrical body 52 so as to raise a resonance frequency to a high frequency. Incidentally, in front (a left side of FIG. 4) of the fixed electrode 59, there is attached a diaphragm ring including a spacer ring and a diaphragm, which faces the fixed electrode 59 (not shown in the figure). The fixed electrode 59 and the diaphragm are disposed at a predetermined interval.
However, the volume reduction filling member 60 for a microphone shown in Japanese Patent Application Publication No. 2011-9807 is formed by a hard plastic sintered porous body. Therefore, in the conventional unidirectional condenser microphone, there is an inconvenience that it is difficult to concentrate a stress in such a way as to uniformly press a unit component member side against an opposite center portion 62.
In view of the aforementioned problem of a conventional technology, the present invention has an object of providing a volume reduction filling member for a microphone which can uniformly press by concentrating the stress on a fixed electrode side while preventing the generation of the cavity resonance of the unidirectional condenser microphone. Moreover, the present invention has an object of providing a unidirectional condenser microphone unit incorporating the volume reduction filling member for a microphone.
Further objects and advantages of the invention will be apparent from the following description of the invention.